At the moment when the car is fully electrified, in addition to battery life anxiety, the most concerned point for consumers is battery safety. We have heard too many news of spontaneous combustion of electric vehicles, so is there any way to control the occurrence of spontaneous combustion or early warning.
At present, the mainstream power battery is divided into ternary lithium battery and lithium iron phosphate battery, the former since its advent in the 1970s, has been rapid development, because of its large specific energy, high output voltage, long cycle life and other advantages, has been widely used in digital, home appliances and other aspects. In the past 10 years, lithium-ion batteries have developed rapidly in electric vehicles and electrochemical energy storage. However, compared with lithium iron phosphate batteries, ternary lithium itself has a safety hazard that cannot be ignored.
With the improvement of indicators such as the energy density of lithium-ion batteries, the safety problems of lithium-ion batteries have become more and more acute. Battery safety issues have received widespread attention in recent years, and improving the safety performance of lithium-ion batteries has also become an important direction for battery research and development. At present, the improvement of the safety performance of lithium-ion batteries, on the one hand, focuses on the improvement of the battery monomer production process, by adding electrolyte additives, improving the structure of positive and negative electrode materials, improving the preparation process of separators, etc., so as to improve safety; on the other hand, considering that the battery thermal runaway process is accompanied by changes in voltage, internal resistance, temperature and other parameters, and accompanied by the generation of characteristic gases, such parameters are used as fault identification parameters, and the introduction of battery thermal runaway early warning mechanism is also an important means to improve battery safety at present.
Recently, it was reported that Metis Engineering released a beta version of its production of battery safety sensors, which perform better than the battery management system (BMS) and are designed to monitor the health of the battery. Not only does the sensor provide early detection of thermal runaways, providing more time for vehicle evacuation, but the data from the sensors can also provide a true picture of the health of the battery and the condition inside the battery pack.
The sensor is designed to acquire a range of environmental parameters, including volatile organic compounds (VOCs), pressure changes, humidity, dew point, and an optional accelerometer to record impact loads. This data can be used to cross-check with other inputs, such as battery temperature, to check for battery exhaust. The sensor also relays data to a control unit, such as a vehicle's ECU, via a configurable CAN interface to alert the driver that the battery has been vented. Not only that, but the sensor can also trigger the process of cutting off the circuitry of the battery pack, giving it a chance to cool down to prevent thermal runaway.
The battery pack becomes hot when charged and discharged. To prevent overheating, most packages are cooled in some way. If the batteries are cooled below ambient temperature, they may drop below the dew point (air cannot carry moisture and condenses to the temperature of a cooler surface), which can lead to short circuits and thermal management problems. Metis battery safety sensors will monitor the dew point in the battery pack and trigger a warning before condensate appears on the battery terminals.
On the whole, the current early warning system is mostly by monitoring temperature, flue gas parameters and combined with voltage, current, internal resistance and other parameters to warn of the emergence of thermal runaway, with multiple parameters for early warning can effectively improve the reliability of the early warning system, reduce its false alarm rate. In the future, in addition to early warning, the best way is to avoid risks as much as possible from the material and design.